Speculations about the Gravity Shield Engine.

Disclaimer: Students who read this are
forewarned that it is informal speculation, not hard
science. It deals with things such as gravity shields
which may not even be possible in our world.

Warning! Do not try to build a gravity
shield at home. Consider the unintended consequences if it
should actually work, though that outcome is highly unlikely.
H. G. Wells played with the idea (fictionally only) in his
1901 book The First Men in the Moon. It supposes that
a gravity shielding material, called "cavorite" might be used
in a flying machine, and even to lift a flying mchine to the moon.
You can read about one unintended consequence in Chapter 2.

Elementary observations.

Most people look at this puzzle and respond quickly in
several ways:

If the wheel were to experience a
rotation through a small angle, it would be the same in
every respect as it was before. So we have no reason to
expect it to initiate such rotation of its own accord.

Stevin's principle shows that it won't work.

The laws of thermodynamics show that it won't work.

These are true, of course. But they fail to tell us exactly
which assumption of the proposal or its description
was a fault, and which fundamental laws of physics it
might violate.

Then there's these somewhat more interesting observations:

If the wheel of the diagram is imagined to be rotated clockwise from a stationary position, through a small angle, to a new stationary position, a small sector of mass near the top moves from a region where its mass is effectively zero (on the left top) to a region where it again has "normal" mass (at the right top). But at the same time an equal sector of mass has been moved from the bottom right into the shielded space, and loses that same amount of mass. So, whatever static position the wheel assumes, it has the same mass distribution, and there's no change of its center of mass caused by such displacement.

This same argument applies whichever direction the wheel is
rotated, leading us to conclude that the arguments for
"one-way" operation of the uniformly symmetric wheel
version of this machine were flawed.

These observations are based on the fact that the
wheel is solid and cylindrically symmetric, and all parts
of it move at the same velocity. So moving the top of the
wheel necessarily moves the bottom, and all the rest of
the wheel, all at the same rotation speed.

The second observation recalls and refutes the original
rationale/explanation of why this machine should
work, which predicted only one-way operation of the
machine.

But what about the
other form of this engine: the eccentric weight? One who thinks
this ought to work might argue as follows:

If this
one starts at the top, falling in the unshielded region,
it gains speed and attains a certain speed
at the bottom. On entering a completely shielded region it
experiences no gravitational force, so its speed is
unchanged (constant) all the way up. It gains more speed
falling on the right, then going back into the unshielded
region. Thus it begins each cycle with an additional amount
of speed (and kinetic energy) more than when it started the
previous cycle.

This modified machine casts serious doubt
that our previous "solution" can be applied to this
version.

We also observe that this rationale predicts that the wheel
would gain kinetic energy when revolving in one direction,
but lose kinetic energy when moving in the other
direction.

All of this leaves nagging questions. What, exactly, does a
gravity shield do, and is a gravity shield even a possibility?

More detailed observations.

Most folks who have commented to me about this engine say
"Since you can't make a gravity shield, then you can't make
such an engine." Others have said "This machine would work
if there were such a thing as a gravity shield, and since
the machine would violate laws of thermodynamics, this
proves that gravity shields are impossible." I don't think
these are valid arguments even though their conclusions may
in fact be correct.
In the process they may miss more fundamental flaws in the
idea, and miss some fun in considering "what if" scenarios,
straying into the realm of science-fiction.

We know that we can make electric field shields, and even
partial magnetic shields. Is there any fundamental proof
that gravity shields are impossible? There are
experimenters right now (2002 CE) who claim to have built
an apparatus which reduces the gravitational field
slightly in a small region. But their experimental claims
are suspect. Theoreticians produce very persuasive
arguments why such a shield is impossible. We'll let the
theoreticians and experimentalists argue about this one.
In our usual spirit of generosity to inventors, let's
grant that somehow they could obtain a gravity shield.
Could they use it to make a perpetual motion device? Suppose that
part of the region above the shield is really gravity-free or at
least has significantly reduced gravitational field.

Just what would a gravitational shield do?

So what's new about this PMM device? It's simply the idea of a
"shield field" over a limited region of space. Such a
boundary-limited gravitational field is unknown in nature,
and we have good reasons to think it's not possible.

Since no one has yet made a gravitational shield, and we
don't know whether anyone can, we should rephrase the
question. Just what do we want a gravitational
shield to do?

We want it to reduce (or increase) the effective
gravitational force in a localized region of space, in
particular, in the region encompassing just part of the
path of a mass moving in a closed path. This is a modest goal.
We don't need a perfect or complete shield. One way we
might imagine to do this is with a device that produces
another gravitational field strictly localized in that
finite localized region of space.

Field shields must also obey the
fundamental laws of physics. "Magical" shields are not allowed.

If the fundamental principle of vector addition of forces is
still valid, then this field of the shield, together with the earth's
gravitational field, would allow us to have part of
the path of the moving mass pass through a greater or lesser
strength field than the other part.

Our problem reduces to answering the question: "What energy changes occur as the body passes through the boundary between the fields?" This could be a messy problem. I don't have a simple answer.

I have attempted to avoid calculus or higher mathematics in
these documents. That's difficult, and error-prone. Perhaps in
this case it is impossible. One reader
wanted to dig deeper, and here's a mathematical treatment he wrote.
Analysis of the gravity shield engine,
by Dr. Peter Moomaw. His document helped
me to correct and remove some indefensible comments I had perviously
had in this section of this web page.